Method of making tire molds



$193332 ATTW' H. C. BOSTWICK METHOD OF MAKING TIRE MOLDS Oflginal Filed March 30, 1937 W 7//// B m n w; .2 H a 7.7 M w; 5 M 2 www f/ A Dec. 10, 1940.

Patented Dec. 10, 1940 METHOD or MAKING Tuna MOLDS Henry C. Bostwick, Akron, Ohio, assignor to Akron Standard. Mold Com Ohio pany, a corporation of Original application March 30, 1937, Serial No.

133,894. Divided and her 14, 1939, Serial No.

'this' application Novem- 304,445

1 Claim. (c1. ail-1 48.2)

This invention relates to a method of making molds for the manufacture of automotive tires, and the present application comprises a division of my co-pending application, Serial No. 133,894,

5 filed March 30, 1937.

It has been found that tires may be greatly improved as to the prevention or reduction of skidding by forming very narrow transverse grooves or kerfs in the tread. The narrowness of the spaces and the fact that they are bounded by vertical planes is believed to be an important characteristic as the corners of the pads thus produced are less subject to wear in use and thus have been thoroughly provenbut practice has demonstrated that they are effective in materially reducing the skidding.

In forming treads for tires it has been customary to employ ribbed molds, but such molds as heretofore constructed are not adapted for providing the very narrow transverse kerfs desired, and such kerfs have been made by a subsequent sawing operation at considerably increased expense.

An object of the present invention is to provide a method of making molds by means of which the very narrow transverse kerfs may be read- I ily formed without requiring the tire tread to be subjected to a sawing operation, as heretofore described.

I accomplish the foregoing object by utilizing a series of thin steel plates which extend transversely of the peripheral ribs and seat in grooves in such ribs and in the base of the mold. These plates are too thin to be made as an integral casting of the mold metal, but have suflicient stiffness to remain in position and form the desired slots or kerfs in the tire tread. The pres ent application includes as well the method of attaching the plates to the ribs so as to assure a rigid connection therebetween.

In the drawing, Fig. 1 is a cross-section of a vulcanizing mold employing my invention; Fig. 2 is a perspective on a larger scale of a portion of the mold looking at'its interior; Figa 3, and 4 are cross-sections of the mold as indicated by the correspondingly designated lines on Fig. 2; Figs. 5 and 6 are'perspective views of the two forms of steel inserts which may be employed in the mold;

Fig. '7 is a perspective of a tire produced by the mold shown, the tread formation partially indicated continuing about the tire; Fig. 8 is a section I similar to Fig. 3 but illustrating the application of thein'vention toexisting types of molds.

Shown'in Fig.1 is atire mold composed of two members, designated l0" and II, the lower of which may if desired be a stationary part of a mold press, the upper beingmounted .on the lower-end of a, plunger. Cooperating with the two mold members described is a third hollow annular member l5, for the inside of the the, the space within this member being supplied with vulcanizing steam through a suitable passageway, indicated at l6 and I1. The annular members with which my invention is concerned are shown as liners 20 and 2 I set into correspondingly formed annular cavities in the mold members l0 and H.

With a tire indicated at A placed on the inner mold member If: and the mold members l0 and II brought together and steam supplied through the passageways, it will be seen that the tire of Fig. 7 is produced having a tread circumference which is the complement of the liner formation.

Referring now particularly to the liner 2| illustrated in Figs. 2 to 6, 22 indicates a comparatively fiat but. slightly curved annular portion corresponding to the extreme outer periphery of the tire, and 23 an edge flange thereof for'the tire portion which lies adjacent the treads. These mold portions carry suitable ribs, preferably somewhat trapezoidal in cross-section to form the comparatively wide grooves extending circumferentially on the tire. In the particular mold shown, there are longitudinal ribs, periodically offset laterally; one of which is .indicated at 24 and 25 and another at 26 and 21. Short transverse ribs are indicated at 28 and 29. This formation however will vary materially according to the particular arrangement of grooves desired in the tread.

Coming now to the matter of the inserts, with which the present invention is especially concemed, these may -be as indicated in 30, in Figs. 2 to 5 inclusive. Each insert consists of a thin steel plate. Its ends 3| may be inclined toward each other, and in each end may be formed a extend into the longitudinal ribs. For instance, Fig. 2 shows some of the inserts extending into the longitudinal rib portions 21, and others extending between the rib portion 25 and adjacent longitudinal ribs 26. Besides being attached to the plate-like portion 22 by the adhesion of the inserts to the casting, they are also firmly anchored by reason of the flaring ends cntering the ribs and also by means of metal of the ribs occupying the notches 32 of the inserts as illustrated at 35 in Figs. 2 and 3. (The latter figure is a section in a plane along the face of the insert, so that the metal of the cast ribs in front of the insert does not appear, but the full width.

of each rib is indicated partly by broken lines back of the insert.)

The casting illustrated in some of the drawings is a die casting, and while this form of casting may be employed, nevertheless it is obvious that the mold may be cast by standard steel or iron foundry practice as desired.

It is desirable in certain instances to adapt existing molds in conformity with my invention. In Fig. 8 I have illustrated a fragment of an existing mold. The mold has the usual rib formations 24 and 26 similar to those heretofore described. Theside walls of these ribs have been provided with narrow slots I by a sawing, milling or other metal cutting operation. The base wall 22 may be provided with a similar slot 42 if desired. These slots 4| and 42 are parallel walled and of such width, that when the thin parallel walled metal insert 300. is forced into the slots it will be retained therein by the walls of the slot. In other words, the insert has a pressed fit relative to the slots, or itmay be tightened in the slots by peening the ribs against the insert.

From the foregoing it will be seen that my improved mold generally comprises a cast base provided with integrally cast ribs of the same cast metal as the base together witha series of thin rolled plate inserts, which extend from one cast "rib to another to form very thin kerfs in the tires formed by such mold.

It will be seen from the drawing and descrip tion above given that the thin metal inserts are effectively anchored in place in the tire mold as permanently as if they were an integral part thereof; but on the other hand, these inserts may be parallel walled and are much thinner than is practicable to make by an ordinary casting or even a die casting. My method of making the mold, either by casting the metal about the plates or forcing the plates into grooves in the cast ribs, provides a rigid mold structure which forms the narrow transverse kerfs desired at the time of the formation and curing of the tread, and without subsequent operation.

If it is desired to interrupt the straight course of the transverse narrow ribs, without interfering with the narrow character thereof, this may be done by making the insert of a wavy or diverted form in place of being strictly planular. An insert of such character is illustrated at 30, Fig. 6, where adjacent its central region the insert is diverted into an approximately semi-cylindrical loop ll. This offset is intended to illustrate any diversion of the insert without interfering with its parallel opposite faces or its narrow characteristics. The ends may be inclined and notched as at3l, 32, Fig. 6, or they may be straight and normal to the top and bottom edges, as shown in Fig. 8.

It is to be understood that in place of making the mold as a one-piece annular member, it may be made as segments which are combined to make the annular form. Also in place of making the mold as a liner inserted as another casting, it might if desired be a single casting with that portion of themain mold which forms the exterior of the tire on that side.

I claim:

The method of making a tire mold comprising casting a metal base with ribs extending upwardly therefrom, thereafter forming grooves in said ribs, placing in the grooves metal inserts in the form of plates thinner than can be eilectively cast, and peening the ribs against the inserts so as to hold them effectively in place.

HENRY C. BOSTWICK. 

